Page:Popular Science Monthly Volume 71.djvu/532

526 to the relative ionization. The photographic action is due almost entirely to $$\beta$$ rays.

The radioactivity of the radio-elements is not a molecular, but an atomic, property, and the rate of emission of the radiations depends on the amount of the element present and is unaffected by the application of any known physical or chemical forces. In order to explain the emission of positively and negatively charged particles, Rutherford and others consider the radio-elements as undergoing spontaneous changes and that the energy of projection of the α and β rays had previously been stored up in the atom as rapid oscillatory or orbital motion. This breaking up of the atoms is considered to be accompanied by the production of a series of new substances which have distinct physical and chemical properties. For instance, thorium produces an intensely radioactive substance, thorium X, which is soluble in ammonia. Thorium gives rise also to a gaseous product, the thorium emanation, and this is the source of another substance, which is deposited on the surface of bodies in the neighborhood of the thorium, and which is known as the "excited activity" or the "active deposit." If a negatively charged wire is brought into close proximity with thorium salts, the "active deposit" will form upon it. The "active deposit" itself decays into a succession of products.

Following will be given some of the products of the various radioactive elements and some of their properties.